System and method for a differential disconnect electric axle

ABSTRACT

Methods and systems are provided for selectively engaging an electric machine to an electric axle of a vehicle. In one example, a method may include engaging or disengaging the electric machine to a differential of the electric-axle by adjusting pressure in a piston coupled to an axle shaft of the electric-axle via a disconnect clutch.

CROSS REFERENCE TO RELATED APPLICATION

The present application is a continuation of U.S. Non-Provisional PatentApplication No. 16/872,205, entitled “SYSTEM AND METHOD FOR ADIFFERENTIAL DISCONNECT ELECTRIC AXLE”, and filed on May 11, 2020. Theentire contents of the above-listed application are hereby incorporatedby reference for all purposes.

FIELD

The present description relates generally to methods and systems forselectively engaging an electric machine to an electric axle.

BACKGROUND AND SUMMARY

Vehicle manufacturers continually strive to improve fuel economy andreduce emissions while meeting customer expectations for performance anddrivability. A hybrid powertrain may be powered by a combination of aninternal combustion engine and an electric machine, such as an electricmachine. The hybrid powertrain may further include an energy storagedevice to power the electric motor. As an example, the engine may becoupled to a first axle of the vehicle and the electric machine may becoupled to a second axle of the vehicle, also referred as an e-axle. Theelectric machine may provide tractive torque to the second axle of thevehicle for enabling an electric mode of vehicle operation. The electricmachine and the engine may be operated independently or in combinationpursuant to the operating conditions of the vehicle and state of chargeof the energy storage device.

The inventors herein have recognized potential issues with the electricmachine being attached to the e-axle of the vehicle at all times. Duringcertain vehicle operating conditions, such as when the vehicle is solelypropelled via engine torque and power from the electric machine is notdesired, the electric machine may operate in a regenerative mode where aportion of the engine power is used to charge the energy storage devicecoupled to the electric machine. However, the energy storage device maybe completely charged and further efforts to charge the module may causedegradation to the electronic components of the energy storage deviceand the electric machine.

In one example, the issues described above may be addressed by a methodfor an electric-axle, comprising: selectively engaging an electricmachine to a differential of the electric-axle by adjusting pressure ina piston coupled to a first axle shaft of the electric-axle via adisconnect clutch. In this way, by including a pressure actuated pistonto engage or disengage a disconnect clutch, the electric machine may beselectively connected or disconnected to the electric axle.

As one example, an electric machine may be coupled to an axle of avehicle, the electric machine transmitting torque to the vehicle wheelsvia a differential. The electric machine may be coupled to thedifferential via a disconnect clutch. The disconnect clutch may beengaged to the differential via a pressure actuated piston. Uponconditions being met for coupling of the electric machine to the axle,the piston may be pressurized causing the piston to move in onedirection which engages the disconnect clutch to a stub shaft which maymechanically couple an axle shaft to the differential. Conditions forcoupling the electric machine to the axle may include, a desire to drivethe axle via the electric machine (to operate the vehicle at leastpartly using machine torque) or to charge the energy storage devicecoupled to the electric machine. Once the electric machine is engaged tothe axle, a change may be observed in the torque transmitted to theaxle. A degradation of the actuation mechanism may be indicated inresponse to an absence of any change in electric machine speed. Uponconditions being met for decoupling of the electric machine to the axle,the piston may be depressurized and the return spring may extend to pushthe piston in another direction and decouple the disconnect clutch fromthe stub shaft, thereby disconnecting the electric machine from the axleof the vehicle. Once the electric machine is disconnected, the e-axlemay operate as a tag axle without influencing torque delivery to thevehicle wheels.

In this way, by connecting an electric machine to a vehicle axle via adisconnect clutch, the electric machine may be selectivelycoupled/decoupled from a differential. During conditions when the energystorage device is fully charged, the technical effect of decoupling theelectric machine from the differential is that the electronic componentsof the electric machine and the energy storage device may not bedegraded due to attempts to further charge the energy storage device.Further, by changing an e-axle to a tag axle during an unsuccessfulcoupling attempt, degradation of components of the actuation mechanismmay be reduced. Overall, by using a pressure actuated piston system forselectively coupling/decoupling an electric machine, operation of thee-axle may be improved and longevity of the mechanical and electroniccomponents may be improved.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a hybrid powertrain arrangement of a vehicle including anelectric-axle.

FIG. 2 shows an electric-axle including an electric machine coupled to adifferential.

FIG. 3 shows an actuation mechanism for selective engagement of theelectric machine of FIG. 2 to the differential.

FIG. 4 shows a view of a pressure actuated piston system used forengagement of the electric machine of FIG. 2 .

FIG. 5 shows a flow-chart illustrating an example method for selectiveengagement of an electric machine to a differential.

DETAILED DESCRIPTION

The following description relates to systems and methods for controllingengagement of an electric machine to an electric axle of a vehicle via adifferential. An example hybrid vehicle powertrain arrangement includingan electric-axle is shown in FIG. 1 . The electric-axle with an electricmachine coupled to a differential is shown in FIG. 2 . The electricmachine may be selectively engaged to the differential via an actuationmechanism, such as a pressure actuated piston system shown in FIGS. 3and 4 . Based on operating conditions of the vehicle and the electricmachine, a vehicle controller may selectively engage the electricmachine to the differential, such as via the control routine of FIG. 5 .

FIG. 1 shows an example embodiment 100 of a hybrid vehicle 102 includinga four-wheel powertrain. The vehicle 102 may include a first powereddriveline 32 and a second powered driveline 42. The first powereddriveline 32 may include an internal combustion engine 118 connected toa first differential unit 114 via a transmission 116. Engine power maybe delivered to the first differential unit 114 through the transmission116. The drive torque delivered to first differential unit 114 may betransferred through axleshafts 132 and 134 to front wheels 122. Thedrive torque from the engine may be further transferred to rear wheels126 via a drive shaft 140 and a second differential unit 104.

The second powered driveline 42 includes an electric machine 106connected to a second differential unit 104 via an actuation mechanism105 for selectively engaging the electric machine 106 to the seconddifferential unit 104. The actuation mechanism 105 includes a disconnectclutch actuated via a pressure actuated piston. The electric machine 106may be powered by an energy storage device such as a battery. Theelectric machine 106 may also operate in a regenerative mode where aportion of the engine power is used to charge the energy storage module.In the regenerative mode, a portion of the engine torque used to rotatethe axleshafts 136 and 138 may be used to rotate the electric machine106, which may result in charging the energy storage device 108 coupledto the electric machine 106.

Based on vehicle operating conditions and a demand for torque output bythe electric machine 106, machine power may be delivered to the seconddifferential unit 104. The drive torque delivered to second differentialunit 104 may be transferred through axleshafts 136 and 138 to rearwheels 136. The axleshafts 136 and 138 powered by the electric machine106 may constitute an electric-axle (also referred herein as an e-axle).The drive torque from the electric machine 106 may be furthertransferred to the front wheels 122 via the drive shaft 140 and thefirst differential unit 114.

Based on a vehicle operating conditions and a state of charge of theelectric storage device 108, the electric machine may be selectivelyengaged to the second differential unit 104. In one example, in responseto conditions being met for vehicle operation at least partially viatorque supplied from the electric machine 106, the electric machine maybe engaged to the second differential unit 104. In another example,during vehicle operation via torque supplied from the engine, inresponse to a state of charge of the energy storage device 108 poweringthe electric machine 106 being higher than a threshold charge, theelectric machine may be disengaged from the second differential unit104. The second differential unit 104 may include a ring gear engaged toa shaft of the electric machine, one or more spider gears mounted on thering gear, a first side gear coupled to one end of a stub shaft andmeshed with the one or more spider gears, and a second side gear coupledto one end of a second axle shaft and meshed with the one or more spidergears, the second differential unit 104 positioned between a first axleshaft and the second axle shaft. Engaging the electric machine 106 mayinclude increasing air pressure in a piston of an actuation mechanism tomove a stem coupling the piston to the a clutch mounted at one end ofthe first axle shaft in a first direction to engage the disconnectclutch to splines of the stub shaft, and then activating the electricmachine to rotate the ring gear via rotation of the shaft. Disengagingthe electric machine 106 may include, reducing air pressure in thepiston to decompress a return spring coiled around the piston and movethe stem in a second direction to disengage the disconnect clutch fromthe splines of the stub shaft, the second direction opposite to thefirst direction. Details of the actuation mechanism for engagement ofthe electric machine 106 to the differential unit 104 is discussed inrelation to FIGS. 2-4 .

During conditions when the electric machine 106 is disconnected from thesecond differential unit 104, the engine provides torque to both thefirst differential unit 114 and the second differential unit 104 whilethe axleshafts 136 and 138 constitute a tag axle. A tag axle mayincrease the support of the chassis at the rear of the vehicle, allowingfor greater carrying capacity and shock resistance.

Vehicle 102 may further include control system 14. Control system 14 isshown receiving information from a plurality of on-board sensors 16 andsending control signals to a plurality of on-board actuators 18. As oneexample, sensors 16 may include a plurality of pressure, temperature,air/fuel ratio, and composition sensors coupled to various locations invehicle 102. Also, sensors 16 may include sensors coupled to theelectric machine 106 and the energy storage device 108 to sense a speedof rotation of the electric machine 106 and a state of charge of theenergy storage device 108. In addition, sensors coupled to the exteriorof the vehicle system such as rain sensor (windshield sensor) andtemperature sensor may be used to estimate ambient conditions. One ormore cameras may be coupled to the vehicle exterior and/or on thedashboard of the vehicle cabin to capture images of the road ahead ofthe vehicle.

The actuators 18 may include, for example, a plurality of valves, fuelinjectors, throttle, spark plug, etc. The actuators may further includea pressure actuated piston of an actuation mechanism selectivelyengaging the electric machine 104 to the electric-axle. The controlsystem 14 may include a controller 12. The controller 12 may receiveinput data from the various sensors, process the input data, and triggervarious actuators in response to the processed input data based oninstruction or code programmed therein corresponding to one or moreroutines.

FIG. 2 shows an example schematic 200 of an electric-axle 202 includingan electric machine assembly 203 coupled to a differential 240 and agearbox 260. The electric machine assembly 203 may include an electricmachine 204 which drives a first shaft 206 via a rotor. The first shaft206 driven by the electric machine 204 may drive a first gear 208. Thefirst gear 208 may drive a second gear 212 coupled to a second shaft214. The second shaft 214 may be in face sharing contact with a ringgear 220 of the differential 240. In this way, rotation of the electricmachine 204 results in rotation of the first shaft 206 and the secondshaft 214 which in turn engages the ring gear 220 of the differential240. The second shaft 214 may be the pinion gear of the differential 240such that upon rotation of the electric machine 204, the ring gear 220may also rotate via the second shaft 214. The second shaft 214 may becoupled to upper portion of the differential 240 via nuts and boltscoupled to an interface 218.

The e-axle 202 may include a first axle shaft 226 coupled to thedifferential 240 via a stub shaft 232 at one end and to a wheel atanother end 232. The e-axle 202 may further include a second axle shaft228 coupled to the differential 240 at one end and to another wheel atanother end 234.

The stub shaft 232 may be a shorter shaft relative to the first axleshaft 226. The stub shaft 232 may be selectively coupled to the firstshaft at a first end via a disconnect clutch 230 of the gearbox 260. Thefirst end of the stub shaft 232 may include splines that may be engaged(such as interlocked) with the teeth of the disconnect clutch 230. Theother end of the stub shaft 232 may be engaged within the differential240.

The differential 240 may be operated in a first mode with the splines ofthe stub shaft 232 interlocked with the disconnect clutch 230. Uponcoupling the stub shaft 232 to the first axle shaft 226, the first axleshaft 226 may be mechanically coupled to the ring gear 220 of thedifferential 240. Therefore, in the first mode, electric machine torquemay be delivered to the first axle shaft 226 via the differential 240and the stub shaft 232. The gear arrangement between the disconnectclutch 230, the stub shaft 232 and the ring gear 220 is furtherelaborated in FIG. 2 . In the first mode, the first axle shaft 226 andthe second axle shaft 228 may be rotating in the same direction (thespeed of rotation of the first axle shaft 226 may be different from thatof the second axle shaft 228) and the electric machine 204 is connectedto e-axle. Therefore, during operation in the first mode, the electricmachine 204 and the ring gear 220 are rotated, and the first axle shaft226 and second axle shaft 228 form an e-axle.

The differential 240 may be operated in a second mode with the splinesof the stub shaft 232 decoupled from the disconnect clutch 230. Upondecoupling the stub shaft 232 from the first axle shaft 226, the firstaxle shaft 226 may no longer be mechanically coupled to the ring gear220 of the differential 240. Due to the decoupling of the stub shaft 232from the disconnect clutch 230, power is no longer transmitted throughthe stub shaft 232 to the first axle shaft 226. In this mode, thedifferential 240 may differentiate within itself and cause the secondaxle shaft and the stub shaft 232 to spin at the same speed but inopposite directions without rotation of the ring gear while maintainingthe ring gear 220 stationary. The first axle shaft and the second axleshafts may continue to spin in the same directions (at same or differentspeeds). In this way, the differential may be held still allowingrelative motion between two axle shafts. In the second mode, theelectric machine 204 may not be operated and the first axle shaft 226and the second axle shaft 228 may together form a tag axle.

The operation of the differential in the first mode includes engagementof the electric machine 204 to the differential 240 that allow foroperation of the first axle shaft 226 and the second shaft 228 as theelectric-axle 202. While, in the second mode, the electric mot machineor 204 is no longer coupled to the first axle shaft 226 via thedifferential 240, and the first axle shaft 226 and the second axle shaft228 may no longer form an electric-axle. In the first mode, the vehicleis either propelled at least partially via electric machine torque orthe energy storage device coupled to the electric machine 204 may becharged. Rotation of the electric-axle (first axle shaft 226 and thesecond axle shaft 228) while the electric machine is engaged may rotatethe rotor of the electric machine, which may result in charging theenergy storage device with a certain reduction of vehicle speed as thecharging may increase a load of the vehicle. A portion of the energygenerated by the engine that would be used to solely rotate the axle maybe used to rotate the rotor of the electric machine, thereby reducingspeed of rotation of the electric-axle. In the second mode, bydecoupling the electric machine 204 from the differential 240, draglosses during conditions when boost torque is not desired (such as whenthe vehicle is travelling down a slope) is reduced and overcharging ofthe energy storage device is averted.

Engagement of the electric machine 204 to the differential 240 isfacilitated via an actuation mechanism 222 including a pressure actuatedpiston 225. The piston 225 may include a pressure inlet via whichpressurized air may be supplied to the piston 225. The pressurized airmay be supplied to the pressure inlet from an on-board air tank storingcompressed ambient air to be used in vehicle systems (such as airbrakes, suspension systems, etc.).

In the presence of positive pressure airflow through the piston 225 thepiston may be pushed in a first direction, compressing a spring mountedon the piston. A stem connecting the piston 225 to the disconnect clutch230 may also be pushed in the first direction causing the disconnectclutch 230 to move towards the stub shaft 232. Upon contact, thedisconnect clutch 230 may interlock with the splines of the stub shaft232. Once the spines are interlocked with the disconnect clutch, thefirst axle shaft 226 may be mechanically coupled to the differential. Inthe absence of air flow through the pressure inlet into the piston 225,the return spring may be de-compressed causing the piston to move asecond direction, opposite to the first direction causing the stemcoupled to the disconnect clutch 230 to recede. As the stem recedes, thesplines of the stub shaft 232 are decoupled from the disconnect clutch230. When the differential is operating in the first mode, air flowthrough the piston 225 is enabled to interlock the disconnect clutch 230to the stub shaft 232, and the electric machine is coupled to thedifferential 240 to either transmit power to the wheels or charge theenergy storage device. When the differential is operating in the secondmode, air flow through the piston 225 is suspended to decouple thedisconnect clutch 230 from the stub shaft 232, and the electric machineis no longer coupled to the differential 240.

FIG. 3 shows an example 300 of an actuation mechanism 222 for selectiveengagement of an electric machine to a differential 240 coupled to anelectric-axle of a hybrid vehicle system. The differential may include aring gear 220 which receives power from the electric machine via a shaft214 which acts as a pinion gear for the differential 240. Thedifferential may include one or more spider gears 306 mashed with atleast two side gears. The spider gears 306 are mounted on the ring gear220 such that a spider gear 306 may rotate with the ring gear and alsorotate about its own axis.

A first axle shaft 226 includes a disconnect clutch 230 at one enddistal from the wheels. The disconnect clutch 230 may be a dog clutchthat may be interlocked with splines 312 at a first end 314 of a stubshaft 232. The disconnect clutch 230 may be slidable over the first axleshaft 226 via a stem 233 connected to the actuation mechanism 222. Thesecond end 315 of the stub shaft 232 may include a first side gear 316meshed with the spider gears 306 of the differential 240. A second sidegear coupled to the second axle shaft 228 may also be meshed with thespider gears 306 of the differential 240. Relative rotation of thespider gear 306 with the ring gear 220 is translated to the first andsecond side gears and the two side gears may rotate at different speeds.Power from the electric machine is transferred may be the side gears viathe spider gears 306.

An example 400 of the actuation mechanism 222 for engagement of theelectric machine to the differential 240 including a pressure actuatedpiston system is further shown in FIG. 4 . The actuation mechanism 222may include an inlet 224 on one side for pressurized air to enter apiston 225. The inlet 224 may include a valve that may be selectivelyactuated to an open position to supply pressurized air into the pistonor a closed position inhibiting air flow into the piston. In alternateembodiments, the inlet 224 may be coupled to any portion of the piston225. The body of the piston 225 may taper from a left end 412 to a rightend 414. A return spring 304 may be coiled around the piston 225 towardsthe tapering right end 414 of the piston 225. A bracket 337 may encirclethe body of the piston chamber to the left of the return spring 304. Thestem 233 may originate from the bracket 337 and terminate at thedisconnect collar 230. In this way, the stem 233 may mechanically couplethe piston 225 to the disconnect collar 230. A plurality of bolts 424may be used to support the piston 225 within the actuation mechanism222. In one example, the actuation mechanism 222 may be enclosed in ahousing.

The return spring 304 may be in a first position, compressed towards theright end 414 of the piston or in a second position, relaxed towards theleft end of the piston 412. The return spring 304 may be in the firstposition in response to pressurized air being supplied to the piston 225via the inlet 224 causing the piston to be pushed towards the right end414, thereby compressing the spring 304. The return spring 304 may be inthe second position in response to pressurized air not being supplied tothe piston 225 via the inlet 224. The spring 304 may be shifted from thefirst, compressed position to the second position by disabling flow ofpressurized air through the inlet 224 which may cause the piston toretreat towards the left, thereby decompressing the spring 304. Also,the spring 304 may be shifted from the second position to the firstposition by enabling flow of pressurized air through the inlet 224.

The piston may be in a first position when the pressurized air issupplied to the piston causing the piston to move to the right. When thepiston is in the first position, the stem 233 may be shifted towardsright causing the disconnect clutch 230 to also be shifted to the rightof the splines 312, thereby interlocking the disconnect clutch 230 withthe spline 312. In the interlocked condition, the first axle shaft iscoupled to the differential via the stub shaft 232 and power istransmitted from the electric machine to each of the first axle shaftand the second axle shaft through the differential 240. Rotation of theshaft 214 of the electric machine causes power to be transmitted to thering gear 220 of the differential which in turn transfers the power tothe spider gears 306 mounted on the ring gear 220 and then onto the sidegears 316 of the axle shaft causing the first and second axle shafts torotate in coordination. In this way, by connecting an electric machineto a vehicle axle via a disconnect clutch, the electric machine may beselectively coupled/decoupled from a differential such that the energystorage device may not be degraded due to attempts to further charge theenergy storage device

The piston may be in a second position when the pressurized air is notsupplied to the piston causing the return spring to be decompressed andthe piston moving to the left. When in the second position, as seen inFIG. 3 , as the piston shifts to the left, the stem is shifted towardsleft end 412 of the piston 225 causing the disconnect clutch 230 to alsobe shifted to the left of the splines 312, thereby unlocking thedisconnect clutch 230 from the spline 312. In the unlocked condition,the first axle shaft is no longer coupled to the differential and thetransmission of power through the differential may be suspended. As thetransmission of power is suspended, the ring gear and the second shaft214 of the electric machine may not rotate, thereby causingdisengagement of the electric machine from the differential and the axleshaft. The electric machine may no longer supply power to the axleshafts. Since the electric-axle is no longer coupled to the electricmachine, engine power may no longer be transmitted to the electricmachine for charging the energy storage device powering the electricmachine. The first and the second axle shafts may rotate in withouttransmission of machine power through the axle shaft. The rotation ofthe second axle shaft may cause the stub shaft to rotate in a directionopposite to the direction of rotation of the second axle shaft while thering gear is maintained stationary. The electric axle may then become atag axle.

Returning to FIG. 3 , a position of the piston such as the firstposition of the piston when the disconnect clutch is interlocked withthe stub shaft and the second position of the piston when the disconnectclutch is decoupled from the stub shaft may be indicated to the vehicleoperator via an indication in the dashboard. A mechanical switch 442 maybe in contact (ride on) a ramp 335 on the outer diameter of the piston225. Based on the position of the piston, the mechanical switch 442 mayprovide a feedback signal which is communicated on the dashboard to showif the electric machine is connected to the electric-axle or if theelectric motor is disconnected (electric axle working as a tag axle). Asan example, a light in the dashboard may be illuminated only when theelectric machine is coupled to the electric-axle.

In this way, the components of FIGS. 1-4 enable a system for anelectric-axle in an vehicle, comprising: a differential coupled to theelectric-axle between a first axle shaft and a second axle shaft, acontroller with computer-readable instruction stored on non-transitorymemory thereof that when executed enable the controller to: operate thedifferential in a first mode with an electric machine mechanicallycoupled to each of the first axle shaft and the second axle shaft via aring gear of the differential, the ring gear coupled to the first axleshaft via a stub shaft interlocked with a disconnect clutch, and operatethe differential in a second mode without electric machine mechanicallycoupled to each of the first axle shaft and the second axle shaft, thering gear detached from the first axle by decoupling of the stub shaftand the disconnect shaft. The differential may be operated in the firstmode during operation of the vehicle at least partially via torquedelivered to the differential from the electric machine or duringcharging of a battery coupled to the electric machine from a portion oftorque delivered to the differential from an engine, and thedifferential may be operated in the second mode during operation of thevehicle via torque delivered to the differential from the engine withoutcharging the battery.

FIGS. 2-4 are shown to scale, although other relative dimensions may beused, if desired.

FIG. 5 shows an example method 500 for selectively engage an electricmachine (such as electric machine 204 in FIG. 2 ) to a differential(such as differential 240 in FIG. 2 ) coupled to an electric axle of ahybrid vehicle (such as vehicle 102 in FIG. 1 ). The vehicle may bepropelled via engine torque, machine torque, or a combination of enginetorque and machine toque. Instructions for carrying out method 500 andthe rest of the methods included herein may be executed by a controllerbased on instructions stored on a memory of the controller and inconjunction with signals received from sensors of the engine system,such as the sensors described above with reference to FIG. 1 . Thecontroller may employ engine actuators of the vehicle system to adjustengine operation, according to the methods described below.

The method begins at 501 and includes estimating and/or measuringvehicle and engine operating conditions. The operating conditions mayinclude vehicle speed, engine speed and/or load, engine temperature,exhaust temperature, gas pressures, mass air flow, etc. The vehiclelocation may be determined based on inputs from an onboard navigationsystem and/or from an external server. Further, ambient conditions suchas ambient temperature, pressure, and humidity may be estimated.

At 504, a state of charge (SOC) of an energy storage device (such as theenergy storage device 108 in FIG. 1 , also referred herein as battery)powering the electric machine may be estimated. At 506, roadcharacteristics of an upcoming road segment may be optionally estimated.The road characteristics estimated may include slope, speed limit,traffic conditions, etc. As an example, the road characteristics may beobtained from an onboard navigation system such as a global positioningsystem (GPS), a network cloud, a vehicle to vehicle (V2V) or aninfrastructure of vehicle (I2V) connected network based on a destinationof travel as indicated by the operator or as predicted by the controllerbased on a travel history of the operator. Step 506 may be an optionalstep and may not be carried out.

At 508, the routine includes determining if conditions are met for thevehicle to be propelled via torque from electric machine. The vehiclemay be either propelled solely via electric machine torque, via acombination of engine torque and electric machine torque, or solely viaengine torque. Conditions where the vehicle may be at least partlypropelled via electric machine torque may include a lower than thresholdtorque demand and a higher than threshold SOC of the battery. Thethreshold torque demand may be pre-calibrated based on the maximumtorque that may be delivered by the electric machine at the estimatedSOC of the battery. As an example, the estimated road conditions in theupcoming route may be considered to predict the torque demand duringtravel in the upcoming road segment. In one example, the torque demandmay be higher if the upcoming route includes climbing a steep slope suchas a hill. The threshold SOC may be the minimum SOC of the batteryneeded for operation of the vehicle.

If it is determined that conditions are met for vehicle operation atleast partially via torque supplied by the electric machine, the routinemay proceed to step 510. The vehicle may be operated via electricmachine torque if the current or upcoming torque demand is lower thanthe threshold torque demand and the SOC of the battery is higher thanthe threshold SOC. At 510, the routine includes determining if theelectric machine is engaged to the differential coupled to anelectric-axle of the vehicle. The electric-axle of the vehicle mayinclude a first axle shaft (such as first axle shaft 226 in FIG. 2 )coupled to the differential via a stub shaft and a second axle shaft(such as second axle shaft 228 in FIG. 2 ) directly coupled to thedifferential.

When the electric machine is engaged to the e-axle via the differential,splines of a stub shaft (such as stub shaft 232 in FIG. 2 ) may beinterlocked with a disconnect clutch (such as disconnect clutch 230 inFIG. 2 ) to mechanically couple the first axle shaft to thedifferential. In order to keep the disconnect clutch interlocked withthe stub shaft, a piston of an actuation mechanism (such as actuationmechanism 222 for the electric mechanism as shown in FIGS. 2-4 ) may besupplied with pressurized air to retain the disconnect clutch in theinterlocked position with the stub shaft. The pressurized air causes thepiston to be moved in one direction such that a stem coupled to thedisconnect clutch is pushed towards the splines of the stub shaft,thereby facilitating interlocking of the disconnect clutch with thesplines of the stub shaft. A shaft (such as a second shaft 214 in FIG. 2) of the electric machine may operate as a pinion for a ring gear of thedifferential and as the first axle shaft is mechanically coupled to thedifferential via the disconnect clutch, torque from the electric machinemay be transferred to the two axle shafts via the differential.

When the electric machine is disengaged from the e-axle, splines of astub shaft may be disconnected from the disconnect clutch tomechanically decouple the first axle shaft from the differential. Inorder to keep the disconnect clutch disconnected from the stub shaft,air supply to the piston of the actuation mechanism may be suspended. Inthe absence of pressurized air, the return spring causes the stemcoupled to the disconnect clutch to move away from the splines of thestub shaft, thereby maintaining the disconnect clutch decoupled from thesplines of the stub shaft. Due to the first axle shaft beingdisconnected from the differential, the electric machine may no longertransfer torque to the axle shafts via the differential and is thereforedisengaged from the e-axle.

If it is determined that the electric machine is already engaged to thee-axle via the differential, at 512, the vehicle may be partially orcompletely operated with machine torque. Operating with machine torqueincludes transmitting power from the electric machine to thedifferential via a shaft coupled to the electric machine and then thepower may be supplied to the wheels via the two axle shafts coupled to afirst set of wheels. The drive torque from the electric machine may befurther transferred to a second set of wheels via a drive shaft andanother differential unit coupled to the second set of wheels.

If it is determined that the electric machine is not already engaged tothe e-axle, at 514, the electric machine may be engaged to the e-axlevia the differential. In order to transmit power from the electricmachine to the two axle shafts, the first axle shaft is to be engagedwith the stub shaft which is coupled to the differential for powertransfer from the electric machine to the axle shafts. The controllermay send a signal to an actuator at an inlet of the piston to open theinlet and allow pressurized air to enter the piston. Also, flow ofpressurized air from the vehicle's on-board air system to the inlet maybe started. A pressure is built in the piston of the actuation mechanismby the supply of pressurized air to the piston via the air inlet. Oncethe air pressure in the piston reaches a higher pre-determined pressurelevel, the piston is moved in a first direction that pushes a stemcoupled to disconnect clutch to be pushed in the first direction towardsthe splines of the stub shaft. Upon contact of the disconnect clutch andthe splines of the stub shaft, the disconnect clutch may be interlockedwith the splines of the stub shaft. The movement of the piston in thefirst direction may cause the return spring to be compressed. Uponengagement of the disconnect clutch and the stub shaft, the flow pathfor torque to reach the axle shafts from the electric machine iscompleted. The electric machine may then be operated to supply torque tothe axle shafts via the differential. Operating the vehicle withelectric machine torque includes transmitting power from the electricmachine to the differential and then supplying the power to the wheelsvia axle shafts coupled to a first set of wheels. Rotation of a rotor ofthe electric machine causes power to be transmitted to the ring gear ofthe differential which in turn transfers the power to the spider gearsmounted on the ring gear and then onto the side gears of the axle shaftcausing the first and second axle shafts to rotate in coordination. Thedrive torque from the electric machine may be transferred to the secondset of wheels via the drive shaft and another differential unit coupledto the second set of wheels.

Upon engagement of the electric machine, at 516, the routine includesdetermining if a change is detected in torque delivered to the axleshafts. Once the electric machine is engaged, due to the transmission ofpower from the electric machine to the axle shafts, there may be atleast a transient change in the torque delivered to the axle shafts. Thechange may include a transient decrease in torque as a new source oftorque (electric machine) is being introduced. Coupling of the electricmachine to the axle via the differential may cause certain transientlosses in torque due to friction which may manifest as a change intorque delivered to the axle shafts. If it is determined that there is atransient change in torque delivered to the axle shafts upon operationof the axle shafts coupled to the electric machine as an e-axle, it maybe inferred that the engagement of the electric machine to the e-axlevia the differential has been successful and power is being transferredfrom the electric machine to the axle shafts. Therefore, at 518, it maybe indicated that the actuation mechanism has not been degraded.

If it is determined that a transient change is not observed in torquedelivered to the axle shafts, it may be inferred that power is not beingtransmitted from the electric machine to the axle shafts. Uponunsuccessful engagement of the electric machine, the mechanism mayoperate as a failsafe and the e-axle may operate as a tag axle. At 520,it may be indicated that there is a degradation in the actuation systemfor engagement of the electric machine to the e -axle via thedifferential. A flag such as a diagnostics code may be set indicatingthe degradation. Due to the inability of engaging the electric machineto the e-axle, at 522, the vehicle may be operated with engine torque.As the e-axle is operated as a tag axle, undesired charging of thebattery coupled to the electric machine may be hindered, therebyaverting degradation of the electrical components of the electricmachine.

Returning to step 508, If it is determined that the conditions are notmet for vehicle operation at least partially via electric machinetorque, the routine may proceed to step 524. The vehicle may not beoperated via electric machine torque if the current or upcoming torquedemand is higher than the threshold torque demand and/or the SOC of thebattery is lower than the threshold SOC. At 524, the current vehicleoperation may be continued with engine torque. Air and fuel may becombusted in the engine to provide power to propel the vehicle.

At 526, the routine includes determining if charging of the battery isdesired with the electric machine being engaged to the e-axle via thedifferential. During vehicle operation via engine torque, the on-boardbattery powering the electric machine may be charged. Rotation of theaxle shafts while the electric machine is engaged may rotate the ringgear of the differential which in turn may cause rotation of the rotorof the electric machine. Rotation of the rotor of the electric machinemay result in charging the battery. A portion of the energy supplied tothe axle shafts from the engine that would be used to solely rotate theaxle may be used to rotate the rotor of the electric machine, therebyreducing speed of rotation of the electric-axle and charging thebattery. However, if the battery is already completely charged furtherattempts to charge the battery may cause degradation of the electricalcomponents of the battery and the electric machine. Therefore, batterycharging may not be desired if the battery is already fully charged.

If it is determined that battery charging is not desired, at 528, theelectric machine may be disconnected from the e-axle. The electricmachine torque may be reduced gradually prior to disengagement of theelectric machine. In order to disconnect the electric machine from thedifferential to inhibit battery charging by regeneration, the first axleshaft is to be disengaged from the stub shaft which is coupled to thedifferential. The controller may send a signal to the actuator of theair inlet to gradually close the inlet, and inhibit air flow into thepiston. The pressure in the piston of the actuation mechanism may begradually decreased by tapering off the supply of pressurized air viathe air inlet. Once the air pressure in the piston reduces to below alower pre-determined pressure level, the spring may be decompressedwhich may cause the piston to move in a second direction, opposite fromthe first direction. The movement of the piston in the second directionmay cause the disconnect clutch coupled to the piston via a stem to moveaway from the splines of the stub shaft, causing disengagement of thestub shaft from the first axle shaft. Upon disengagement of thedisconnect clutch and the stub shaft, the flow path for charging of thebattery is severed.

If it is determined that battery charging is desired, at 530, theonboard battery may be charged via rotation of the electric machinerotor with the rotation of the axle shafts. In one example, if theelectric machine is not engaged to the e-axle and it is determined thatcharging of the on-board battery is desired during vehicle operation viaengine torque, the electric machine may be engaged to the e-axlefollowing the method elaborated in step 514 and then charging of thebattery may be carried out.

In this way, system for a vehicle may comprise a pressure actuatedmechanism for coupling an electric machine to an electric-axle via adifferential, a first axle shaft coupled to the differential via a stubshaft and a second axle shaft directly coupled to the differential, thestub shaft including splines interlocked with a disconnect clutchcoupled to the actuation mechanism. By using a pressure actuatedmechanism for selectively coupling/decoupling an electric machine,operation of the e-axle may be improved and degradation of themechanical and electronic components may be reduced.

An example method for an electric-axle comprises: selectively engagingan electric machine to a differential of the electric-axle by adjustingpressure in a piston coupled to a first axle shaft of the electric-axlevia a disconnect clutch. In any preceding example, additionally oroptionally, the selective engagement includes, in response to conditionsbeing met for vehicle operation at least partially via torque suppliedfrom the electric machine, engaging the electric machine to thedifferential. In any or all of the preceding examples, additionally oroptionally, the selective engagement further includes, during vehicleoperation via torque supplied from an engine, in response to a state ofcharge of an energy storage device powering the electric machine beinghigher than a threshold charge, disengaging the electric machine fromthe differential. In any or all of the preceding examples, additionallyor optionally, the differential includes a ring gear engaged to a shaftof the electric machine, one or more spider gears mounted on the ringgear, a first side gear coupled to one end of a stub shaft and meshedwith the one or more spider gears, and a second side gear coupled to oneend of a second axle shaft and meshed with the one or more spider gears,the differential positioned between the first axle shaft and the secondaxle shaft. In any or all of the preceding examples, additionally oroptionally, engaging the electric machine includes, increasing airpressure in the piston to move a stem coupling the piston to thedisconnect clutch mounted at one end of the first axle shaft in a firstdirection to engage the disconnect clutch to splines of the stub shaft,and then activating the electric machine to rotate the ring gear viarotation of the shaft. In any or all of the preceding examples,additionally or optionally, engagement of the electric machine includestransmission of torque from the electric machine to the first axle shaftvia each of the shaft of the electric machine, the ring gear of thedifferential, the one or more spider gears, the first side gear, thestub shaft, and the disconnect clutch. In any or all of the precedingexamples, additionally or optionally, engagement of the electric machinefurther includes transmission of torque from the electric machine to thesecond axle-shaft via each of the shaft of the electric machine, thering gear of the differential, the one or more spider gears, and thesecond side gear, wherein each of the stub-shaft, the first axle shaft,and the second axle-shaft rotates in a same direction. In any or all ofthe preceding examples, additionally or optionally, moving the stem inthe first direction compresses a return spring coiled around the piston.In any or all of the preceding examples, additionally or optionally,disengaging the electric machine includes, reducing air pressure in thepiston to decompress the return spring and move the stem in a seconddirection to disengage the disconnect clutch from the splines of thestub shaft, the second direction opposite to the first direction. In anyor all of the preceding examples, additionally or optionally,disengagement of the electric machine includes each of the shaft of theelectric machine and the ring gear being at rest without transmission oftorque from the electric machine to the differential, and the stub shaftand the second axle-shaft rotating in opposite directions. In any or allof the preceding examples, the method further comprising, additionallyor optionally, prior to disengaging the electric machine, reducing atorque delivered from the electric machine, and then reducing the airpressure in the piston. In any or all of the preceding examples,additionally or optionally, increasing the air pressure includessupplying pressurized air to the piston via an inlet housed in thepiston and wherein reducing air pressure in the piston includessuspending supply of pressurized air to the piston. In any or all of thepreceding examples, the method further comprising, additionally oroptionally, in absence of a change in torque delivered to each of thefirst axle shaft and the second axle shaft upon engagement of theelectric machine, indicating degradation of the electric-axle, andoperating the vehicle solely via torque supplied from the engine.

Another system for a vehicle comprises: a pressure actuated mechanismfor coupling an electric machine to an electric-axle via a differential,a first axle shaft coupled to the differential via a stub shaft, and asecond axle shaft directly coupled to the differential, the stub shaftincluding splines interlocked with a disconnect clutch coupled to theactuation mechanism. In any preceding example, additionally oroptionally, the electric machine drives a pinion of a ring gear of thedifferential, the ring gear coupled to the stub shaft via one or morespider gears and a first side gear. In any or all of the precedingexamples, additionally or optionally, the pressure actuated mechanismincludes a piston, a return spring coiled around a portion of thepiston, a stem originating from the piston and terminating in thedisconnect clutch, and an air inlet coupled to the piston. In any or allof the preceding examples, additionally or optionally, the piston movesto a first position upon air pressure in the piston reaching a firstthreshold pressure shifting the disconnect clutch to interlock with thesplines of the stub shaft, and wherein the piston moves to a secondposition upon air pressure reducing to a second threshold pressuredecoupling the disconnect clutch from the splines.

In yet another example, a system for an electric-axle for in vehiclecomprises: a differential coupled to the electric-axle between a firstaxle shaft and a second axle shaft, a controller with computer-readableinstruction stored on non-transitory memory thereof that when executedenable the controller to: operate the differential in a first mode withan electric machine mechanically coupled to each of the first axle shaftand the second axle shaft via a ring gear of the differential, the ringgear coupled to the first axle shaft via a stub shaft interlocked with adisconnect clutch, and operate the differential in a second mode withoutelectric machine mechanically coupled to each of the first axle shaftand the second axle shaft, the ring gear detached from the first axle bydecoupling of the stub shaft and the disconnect shaft. In any precedingexample, additionally or optionally, the differential is operated in thefirst mode during operation of the vehicle at least partially via torquedelivered to the differential from the electric machine or duringcharging of a battery coupled to the electric machine from a portion oftorque delivered to the differential from an engine, and wherein thedifferential is operated in the second mode during operation of thevehicle via torque delivered to the differential from the engine withoutcharging the battery. In any or all of the preceding examples,additionally or optionally, the controller includes further instructionwhen executed enable the controller to: transition from the first modeto the second mode by reducing air pressure in a piston coupled to thedisconnect clutch causing the piston to move the disconnect clutch awayfrom the stub shaft.

FIGS. 2-4 show example configurations with relative positioning of thevarious components. If shown directly contacting each other, or directlycoupled, then such elements may be referred to as directly contacting ordirectly coupled, respectively, at least in one example. Similarly,elements shown contiguous or adjacent to one another may be contiguousor adjacent to each other, respectively, at least in one example. As anexample, components laying in face-sharing contact with each other maybe referred to as in face-sharing contact. As another example, elementspositioned apart from each other with only a space there-between and noother components may be referred to as such, in at least one example. Asyet another example, elements shown above/below one another, at oppositesides to one another, or to the left/right of one another may bereferred to as such, relative to one another. Further, as shown in thefigures, a topmost element or point of element may be referred to as a“top” of the component and a bottommost element or point of the elementmay be referred to as a “bottom” of the component, in at least oneexample. As used herein, top/bottom, upper/lower, above/below, may berelative to a vertical axis of the figures and used to describepositioning of elements of the figures relative to one another. As such,elements shown above other elements are positioned vertically above theother elements, in one example. As yet another example, shapes of theelements depicted within the figures may be referred to as having thoseshapes (e.g., such as being circular, straight, planar, curved, rounded,chamfered, angled, or the like). Further, elements shown intersectingone another may be referred to as intersecting elements or intersectingone another, in at least one example. Further still, an element shownwithin another element or shown outside of another element may bereferred as such, in one example.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The control methods and routines disclosed herein may be stored asexecutable instructions in non-transitory memory and may be carried outby the control system including the controller in combination with thevarious sensors, actuators, and other engine hardware. The specificroutines described herein may represent one or more of any number ofprocessing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various actions,operations, and/or functions illustrated may be performed in thesequence illustrated, in parallel, or in some cases omitted. Likewise,the order of processing is not necessarily required to achieve thefeatures and advantages of the example embodiments described herein, butis provided for ease of illustration and description. One or more of theillustrated actions, operations, and/or functions may be repeatedlyperformed depending on the particular strategy being used. Further, thedescribed actions, operations, and/or functions may graphicallyrepresent code to be programmed into non-transitory memory of thecomputer readable storage medium in the engine control system, where thedescribed actions are carried out by executing the instructions in asystem including the various engine hardware components in combinationwith the electronic controller.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. The subject matter of the present disclosure includes allnovel and non-obvious combinations and sub-combinations of the varioussystems and configurations, and other features, functions, and/orproperties disclosed herein.

As used herein, the term “approximately” is construed to mean plus orminus five percent of the range unless otherwise specified.

The following claims particularly point out certain combinations andsub-combinations regarded as novel and non-obvious. These claims mayrefer to “an” element or “a first” element or the equivalent thereof.Such claims should be understood to include incorporation of one or moresuch elements, neither requiring nor excluding two or more suchelements. Other combinations and sub-combinations of the disclosedfeatures, functions, elements, and/or properties may be claimed throughamendment of the present claims or through presentation of new claims inthis or a related application. Such claims, whether broader, narrower,equal, or different in scope to the original claims, also are regardedas included within the subject matter of the present disclosure.

1. A method for an electric-axle of a vehicle, comprising: selectivelymechanically coupling an electric motor and a differential of theelectric-axle through operation of an actuation system that is coupledto a disconnect clutch which is coupled to a first axle shaft of theelectric-axle based on a state of charge of an energy storage device;wherein the disconnect clutch includes splines that engage and disengageto mechanically couple and decouple the electric motor from thedifferential.
 2. The method of claim 1, wherein selectively mechanicallycoupling the electric motor and the differential includes disengagingthe disconnect clutch when the state of charge of the energy storagedevice is greater than a threshold value.
 3. The method of claim 2,wherein selectively mechanically coupling the electric motor and thedifferential includes engaging the disconnect clutch when the state ofcharge of the energy storage device is less than the threshold value. 4.The method of claim 1, further comprising selectively mechanicallycoupling the electric motor and the differential through operation ofthe actuation system based on actuation system degradation.
 5. Themethod of claim 4, wherein selectively mechanically coupling theelectric motor and the differential through operation of the actuationsystem based on actuation system degradation includes disengaging thedisconnect clutch when it is determined that the actuation system isdegraded.
 6. The method of claim 1, wherein the actuation systemincludes a piston that is fixedly coupled to one of the splines via astem.
 7. The method of claim 6, wherein the piston is actuated via aninlet that receives pressurized air.
 8. The method of claim 6, whereinthe actuation system includes a mechanical switch that interacts with aramp on the piston to determine an engaged state or disengaged state ofthe disconnect clutch.
 9. The method of claim 6, further comprising aspring coupled to the piston.
 10. The method of claim 1, wherein theelectric motor is mechanically coupled to the differential via multipleshafts and gears whose rotational axes are parallel to one another. 11.The method of claim 1, wherein a rotational axis of the electric motoris not parallel the rotational axis of the first axle shaft.
 12. Themethod of claim 1, wherein the vehicle is a hybrid vehicle.
 13. A systemfor an electric vehicle, comprising: a pressure actuated mechanism forcoupling an electric machine to an electric-axle via a firstdifferential; a first axle shaft coupled to the first differential via astub shaft; and a second axle shaft directly coupled to the firstdifferential, the stub shaft including splines interlocked with adisconnect clutch coupled to the pressure actuated mechanism; wherein apiston in the pressure actuated mechanism moves to a first position uponair pressure in the piston reaching a first threshold pressure shiftingthe disconnect clutch to interlock with the splines of the stub shaft;wherein the piston moves to a second position upon air pressure reducingto a second threshold pressure decoupling the disconnect clutch from thesplines; and wherein the electric machine drives a pinion of a ring gearof the first differential, the ring gear coupled to the stub shaft viaone or more spider gears and a first side gear, the electric machinedriving the pinion via a gear pair of a first gear and a second gear,the second gear coupled to the pinion and the first gear coupled to arotor of the electric machine via a first shaft, the pinion and firstshaft mounted parallel to and laterally offset from one another andperpendicular to the first axle shaft and second axle shaft.
 14. Thesystem of claim 13, wherein the pressure actuated mechanism includes amechanical switch that interacts with a ramp on the piston to determinean engagement state or disengagement state of the disconnect clutch. 15.The system of claim 13, wherein the electric vehicle is a hybridelectric vehicle with an internal combustion engine that is coupled to asecond differential.
 16. An electric axle system comprising: a dogclutch that is configured to selectively disconnect an electric motorfrom a differential based on a state of charge of an energy storagedevice; and a mechanical switch coupled to a ramp in a piston of anactuator for the dog clutch and configured to determine an engagementstate of the dog clutch; wherein the dog clutch includes splines thatare coupled to a stub shaft that is rotationally coupled to a first axleshaft.
 17. The electric axle system of claim 16, further comprising acontroller configured to operate the dog clutch to disconnect theelectric motor from the differential when the state of charge of theenergy storage device is greater than a threshold value.
 18. Theelectric axle system of claim 16, further comprising a controllerconfigured to operate the dog clutch to disconnect the electric motorfrom the differential when it is determined that the actuator isdegraded.
 19. The electric axle system of claim 16, wherein the pistonis actuated via pressurized air and the actuator includes a springcoupled to the piston.
 20. The electric axle system of claim 16, whereinthe stub shaft includes a side gear that meshes with a spider gear inthe differential.